Typical balers comprise a frame pulled by a tractor over a field to pick up hay, straw or other crop to be baled and feeding the crop into a baling chamber where it is compressed into bales. One common baler type creates parallelepiped shaped bales that are formed by a plunger which reciprocates inside a baling chamber. When the bales are complete a tying mechanism is actuated to bind the bale before it is ejected from the baler.
Typically the plunger reciprocates in the baling chamber against the crop material when a new charge of crop is introduced into the chamber. Crop is fed into the baler via a crop pick-up assembly located at ground level and a duct communicating between the pick-up assembly and the baling chamber. Crop is typically pre-compressed in the duct into uniform amounts prior to introduction into the baling chamber. A stuffer mechanism then transfers the pre-compressed crop into the baling chamber whenever enough crop material is made available in the duct.
There are four basic types of machine configurations possible with the plunger and stuffer combination. The first type has a continuous plunger, i.e. the plunger is gearbox driven and operates continuously, and a continuous stuffer. With this type of baler crop is continuously fed into a pre-compression chamber by e.g. a three cycle feed rake, each successive cycle filling the chamber and the third cycle moving the flake into the baling chamber where the plunger compresses the flake into a bale. With this continuous plunger-continuous stuffer design there is no guarantee of flake consistency (size, density). The feed rake is mechanically timed with the plunger operation resulting in a flake size that varies depending on how much crop is fed during the three cycles for each plunger stroke. This design does not work well if enough crop cannot be gathered in time to create a full flake. This results in bales that are soft at the top.
The second type of baler design also has a continuous plunger, but uses an intermittent stuffer. Here crop is fed into the pre-compression chamber to form a flake, the flake is then transferred into the baling chamber via an intermittently operating stuffer and then the plunger compresses the flake into the bale. With such continuous plunger-intermittent stuffer designs there is also no guarantee of flake consistency (size, density). For example, when the pre-compression chamber sensor reports that the pre-compression chamber is filled to the specified level, the stuffer may not immediately engage because the continuous plunger is not in the appropriate position. During the time between the pre-compression chamber sensor reporting “ready” and the plunger getting into position, additional crop is building up in the pre-compression chamber. The result is inconsistent flake size and density in the pre-compression chamber due to the system waiting on the plunger to get to the appropriate position. This design avoids the “soft top” as in the previous example but the flake size is still inconsistent.
The third type of known baler design uses an intermittent plunger i.e. the plunger is not gearbox driven but is driven e.g. hydraulically and the stuffer is driven continuously. With this continuous feeding system there is no pre-compression chamber and the crop is delivered directly into the baling chamber via a feed fork. A switch at the top of the bale chamber activates a plunger cycle when the baling chamber fills with crop and exerts pressure on the switch. Here the potential variations in flake size and density occur as the feeder mechanism throws crop up into the baling chamber activating the pressure switch.
The fourth and last type of known baler configuration also uses an intermittently driven plunger e.g. hydraulically driven, and also uses an intermittent stuffer. This type of system provides the greatest level of flake consistency as to size and density, because under ideal circumstances the intermittent plunger is always in the ready position when the signal is received that the pre-compression chamber is full. When the pre-compression chamber sensor indicates that sufficient crop has entered the pre-compression chamber a signal is sent to the intermittent stuffer which immediately begins to move the flake from the pre-compression chamber into the baling chamber. As the stuffer approaches a pre-determined position the plunger movement is started. The result is improved flake consistency. This combination gives the best bale quality by having consistent density from top to bottom (due to the intermittent feed system) and consistent flake sizes (from the intermittent plunger system). With both systems being intermittent, the challenge is to appropriately synchronize the activation of the stuffer with that of the plunger.
With the second type of baler described above (continuous plunger-intermittent stuffer) the components are mechanically linked together and therefore operate at predetermined (non-adjustable) rates/ratios. The goal on machines like this is to match the throughput of the baler to some given ratio which would correspond to accumulating each flake in an exact whole number ratio to machine plunger strokes. Examples of this process are described in U.S. Pat. Nos. 6,474,228 and 6,543,342. With a baler like that of the fourth type described above (intermittent plunger-intermittent stuffer), the components (plunger and stuffer) are not linked together with a mechanical linkage so these ratios are not meaningful, instead the goal is to accumulate the predetermined flake of material so that the system, i.e. the combination of the stuffer and the plunger, runs continuously i.e. without any wait time.
With mechanically linked balers as described above, having a continuous plunger drive and an intermittent stuffer drive, the stuffer mechanism has the same cycle rate as the plunger and is typically driven through a one revolution clutch. This clutch is mechanically timed to the plunger so that the plunger is not covering the top opening of the accumulating duct when the stuffer is activated and so that the plunger begins compressing the flake and covers this opening before the stuffer retracts and returns to its home position. If the plunger travels just past the point that the one revolution clutch can be engaged when the chamber full signal is received, the chamber must continue receiving crop material for almost one full plunger cycle before the stuffer can be activated to lift the flake out of the duct and into the baling chamber. If set for maximum throughput, the duct (pre-compression chamber) cannot continue receiving material for this amount of time and the baler will plug. Ideally the chamber full signal is received just before the plunger reaches the point in its cycle that the one revolution clutch can be activated. This is the reason that integer ratios of pre-compression chamber fill time to plunger cycle time should be attained to avoid plugging the baler.
The problem with balers such as those described in U.S. Pat. Nos. 6,474,228 and 6,543,342 is that there are discrete areas of the function that must be avoided to prevent plugging of the machine. For example, one embodiment uses a ratio Tf/Tp (where Tf is the time required to fill the chamber to the desired density, and Tp is the cycle time of the plunger). For maximum throughput this ratio should be 1. However, plugging problems can occur if this ratio is just above 1 or just above 2 or just above 3 etc. Therefore, if the ratio was just below 2 (an acceptable operating range) maximum throughput is not being achieved so the vehicle speed should be increased, but by increasing the speed the value of the ratio will begin to drop and as it passes through values just above 1 plugging can occur.
In another embodiment described in the above-referenced patents, a value of (Ts−Tf)/Ts is generated (where Ts is the cycle time of the stuffer mechanism). The problem with using this value as a control for the propelling vehicle speed is that this produces a discontinuous function and multiple Tf values will give the same ratio value (because Ts is an integer multiple of Tp and increases to the next multiple if Tf would be greater that Ts). Therefore if the resulting value is in the range that could be produced with multiple values of Tf, the system does not know which segment of the curve it is on without some additional information (it must know what multiple of Tp is being used). Also the problem stated above applies here as well, values of Tf that lie just beyond the discontinuities of the graph can cause plugging problems and need to be avoided.
Accordingly, there is a clear need in the art for a method for maximizing the throughput of a baler without the aforementioned problems.